Some power plant systems, for example certain nuclear, simple cycle and combined cycle power plant systems, employ turbines in their design and operation. Some of these turbines operate at high temperatures and include rotors (e.g., a drum rotor, a wheel and diaphragm rotor, etc.) that are in direct contact with high temperature steam which may reduce the lifespan of the rotor and rotor components (e.g., buckets). These buckets are installed circumferentially about the rotor via a set of entry slots in the rotor posts and/or rims. One area of the rotor that experiences severe environmental conditions (e.g., temperatures, pressures, etc.) during operation, is the forward rotor post which is located forward of the first stage bucket. During turbine operation, the forward rotor post may creep away from the first stage bucket due to centrifugal and bending loads exerted by the first stage bucket. This creep effect may open a dovetail slot in the rotor which restrains the first stage buckets, possibly resulting in the first stage buckets becoming loose.
FIGS. 1-3 show schematic cut-away views of prior art turbine systems. FIGS. 1-2 show a prior art turbine system 50 including a stator 52 and a rotor 54 substantially defining a working fluid flow path 7 (e.g., steam flow path). Rotor 54 illustrated in FIG. 1 includes a plurality of buckets 70 disposed between a plurality of vanes 78, the buckets 70 including a first stage bucket 72 disposed in a dovetail slot 80 between a first rotor post 82 and a second rotor post 84. During operation, as shown in FIG. 2, a force imbalance 41 (e.g., a bending moment) may be exerted on first rotor post 82 as a first side 92 of first rotor post 82 is not acted upon by a bucket load and a second side 94 of first rotor post 82 is acted upon by a bucket load from first stage bucket 72. Some prior art systems, as shown in FIG. 3, increase an axial length 1′ of first rotor post 82 in order to compensate for force imbalance 41 (indicated in FIG. 2), this increased length guarding against creep deflection and axial opening of dovetail slot 80. During operation, fluid flow through working fluid flow path 7 (shown in FIG. 1) may contact first stage bucket 72 and impart a force on the rotor. However, increasing length L of first rotor post 82 to counter the forces imparted on the rotor by first stage bucket 72 may require increased axial rotor span and other design considerations which may place constraints on turbine design and manufacture.